Federal investigators will focus on whether a CTA train operator fell asleep at the controls and if an automatic braking system was working properly as they seek to pinpoint the cause of a spectacular crash Monday that left a Blue Line car perched atop an escalator.

The operator may have fallen asleep shortly before her train smashed through a “bumper” at the end of the track at O’Hare International Airport just before 3 a.m., according to a transit union representative.

The driver, whose name has not been released, told people she nodded off moments before the crash, said Robert Kelly, president of Amalgamated Transit Union Local 308.

“I can confirm that she was extremely tired,” Kelly said. “Indications are she might have dozed off.”

Other crucial issues that will come under sharp focus in the inquiry include whether the train was speeding as it entered the station at the airport and whether the safety control system was working.

The train was traveling with such momentum that it smashed through a barrier designed to stop trains at the end of the line, jumped the platform and climbed up the escalator.

More than 30 people were hurt, though none of the injuries was considered life-threatening, officials said. Had the incident occurred at any time other than the middle of the night, scores could have been killed or injured, experts said.

Blue Line service to the airport will be halted until authorities finish studying the crash site and decide how to remove the wreckage. The CTA late Monday declined to say when the station might reopen.

The National Transportation Safety Board is investigating the incident, which temporarily halted commuter rail service to one of the country’s busiest airports. The CTA is shuttling passengers to O’Hare from the nearby Rosemont stop for the time being.

The front car of the eight-car train remained wedged atop the escalator late Monday.

“The train is not going to go anywhere for the foreseeable future,” said Tim DePaepe, an NTSB railroad accident investigator. “We need to examine the train and the position it’s in prior to its movement.”

The NTSB will also will try to determine how fast the train was going when the crash occurred. Officials said the train did not carry an event data recorder. Typically, the CTA’s older-model 2600 series cars, like the ones in Monday’s crash, do not have event recorders.

The train, however, did have an outward facing video system, DePaepe said, and officials are reviewing the tape and several others. They also are examining the signals and tracks to see if there were problems or malfunctions.

The crash happened around 2:50 a.m., one of the station’s lightest traffic times.

“I heard a boom and when I got off the train, the train was all the way up the escalator. It’s a wreck,” Denise Adams, who was riding toward the back of the train, told reporters. “It was a lot of panic because it was hard to get people off the train.

CTA President Forrest Claypool said safety is the agency top priority. “We run half a million train trips a year,” he said. “So when something like this happens we want to work closely with our engineers and theirs (the NTSB) to get to the very bottom of this as fast as we can.”

Kelly speculated that the bumping post acted as a catapult, shooting the train off the track. The impact could have caused the operator’s hand to push forward on the lever that sends power to the train, surging it forward and launching it, he said.

“I think what happened is, when she hit the post, the hand went up, whether she was caught off guard, whatever it was,” Kelly said at a news conference.

The driver has been employed with CTA for about a year, Kelly said. She “works a lot of overtime,” he said, but she had been off for about 17 hours before starting her overnight shift, which began at 8 p.m. on Sunday.

“So she had an ample amount of time to be off that day,” Kelly said. “I do know she works a lot, as a lot of our members do.”

After the crash, she immediately got out of the train and started checking on passengers, Kelly said. She was later treated for an injured leg but was released from the hospital Monday.

The train operator had not yet been interviewed by the NTSB, DePaepe said. Federal authorities will look into her work schedule, her activities in the week leading up to the crash and her medical background as part of their investigation, DePaepe said. She also will undergo routine drug and alcohol testing.

Kelly said he did not believe that the driver was speeding when she entered the station.

“All the reports that we’ve received from the tower men and the supervisor on duty indicate that she was not coming in at a fast speed at all; she was coming in like every other train, normal,” Kelly said.

Former longtime CTA executives said it appeared the train was going too fast, however.

“I would tend to think she was in excessive speed mode,” said Romayne Brown, who had more than 31 years at the CTA, starting as a rail conductor and working her way up to vice president of rail operations before retiring in 2010. “What would cause her not to reduce speed is the question.”

CTA lines generally have a safety system known as automatic train control, with “trips” to slow or stop a train if it goes through a red signal or is going too fast for conditions, experts said.

Normally, the automatic train control system gives an audible alarm if speed restrictions are violated, giving the operator only seconds to respond or the train stops itself.

Robert Paaswell, a former CTA executive director who is now a professor of transportation at the City College of New York, said equipment should have slowed the train, and warned the operator.

“Only a few things can happen — a failure of the system or she was going too fast.”

Federal investigators will conduct tests and analyze data to determine if the automatic train control system was working near the O’Hare station.

It was unclear, however, whether the train was on a track equipped with system as it approached the O’Hare station.

In a case involving a track that lacks the control system, personnel in the CTA’s nearby control tower are supposed to communicate with the train operator via radio, Brown said. Whether or not a tower man was on duty is unknown.

Even without a data recorder, investigators should be able to determine the train’s speed, she said.

Operating a train is a repetitive task but is not easy and requires much training, Brown said.

“It’s definitely a challenging job that requires you to be astute and attentive,” she said.

The NTSB says employers should establish science-based fatigue management systems to identify factors that cause fatigue and detect its presence before problems occur.

The NTSB is also still investigating another recent CTA collision, which occurred Sept. 30, 2013, when an unattended four-car train plowed into a stopped Blue Line train at the Harlem-Congress Station.

The four-year, $492 million project to overhaul the O'Hare branch of the CTA Blue Line starts this weekend with temporary track closures between the Western and Logan Square stations, the transit agency said Thursday.

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